Heterogeneity of microbiome and flavor profiles of industrial-scale Laotan Suancai: Fermentation craft plays important roles

Laotan Suancai is a well-known Chinese traditional fermented vegetable with a unique flavor. However, there are significant differences in the quality of Laotan Suancai pickled by jars (LTSC-J) and pools (LTSC-P) on an industrial scale. To reveal the effect of fermentation craft on Laotan Suancai quality, the microbial community, flavor metabolites, and physicochemical properties of the two types of Laotan Suancai, as well as their interrelationship were investigated. LTSC-P had higher salinity, glucose content, and histidine content, while LTSC-J had higher TA, lactic acid content, and isobutyric acid content. Nine differential aroma-active compounds were found between the two types of Laotan Suancai: anethole, eucalyptol, diallyl sulfide, estragole, diallyl disulfide, eugenol, linalool, nonanal, and ethyl butyrate. LTSC-P showed a higher relative abundance of Weissella, Acinetobacter, Pseudomonas, Allorhizobium-Neorhizobium-Pararhizobium-Rhizobium, Inhella, and Leuconostoc compared to LTSC-J. Co-occurrence analysis indicated the distinct differences in the co-occurrence patterns of the microbial network across the two types of Laotan Suancai. RDA analysis indicated that glucose, salinity, TA, maltose, and nitrite were the main drivers for the differences in bacterial communities between the two types of Laotan Suancai. Spearman correlation analysis revealed strong correlations between 18 bacteria and 61 flavor compounds. Finally, bacterial metabolic function prediction indicated that sulfide and aromatic ester may be biosynthesized by sulfur metabolism, cysteine and methionine metabolism, pyruvate metabolism, and butanoate metabolism. Overall, these findings provide important guidance for improving the manufacturing and quality of Laotan Suancai.